Local government officials now worry that the Code River, which winds down from Mount Merapi, could channel scorching volcanic mudflows into the city of Yogyakarta 30 kilometers about 19 miles away and have put the city on high alert.

Severe mudflows can also occur as a result of rapid drainage of glacier-dammed lakes due to glacial melting; examples of this phenomenon include the catastrophes in the Sima Valley (Norway) in 1893 and 1937, and in the city of Tyrnyauz (Caucasus) in 1977 and 1992 [5].

Any sign of sustain rainfall is a signal for people to go to evacuation areas as the steep mountain slopes can create massive flash floods of lahar and volcanic mudflows which can rage down slopes carrying with them boulders and the wet cement like 'Lahar flows' that can destroy almost any structure in the path of the fast flowing debris.